1. Technical Field
This disclosure relates generally to a power transmission apparatus designed to transmit power, as produced by an internal combustion engine, to auxiliary devices.
2. Background Art
There are known power transmission systems which work to transmit output power of an internal combustion engine to a given accessory and other accessories mounted in, for example, an automobile using an endless transmitting member such as a belt. The given accessory is, for instance, an engine starter to start the internal combustion engine. The given accessory may be rotated by the output power of the internal combustion engine along with the other accessories in a regenerative mode of operation to generate electricity. Japanese Patent First Publication No. 2001-59555 teaches a power transmission system which has two auto-tensioners to adjust the degree of tension of an endless transmitting member to a required level.
The power transmission system, as disclosed in the above publication, has a first auto-tensioner that is one of the two auto-tensioners. The first auto-tensioner is disposed between a driving pulley connected to the internal combustion engine and a pulley of a given accessory installed in an automotive vehicle to be movable relative to the internal combustion engine for regulating the degree of tension of the endless transmitting member. The given accessory is designed to operate selectively as an engine starter (i.e., an electric motor) and an electric generator. When the given accessory operates as the electric generator in a regenerative mode, the first auto-tensioner works to eliminate the loosening of the endless transmitting member between the given accessory and its pulley. Alternatively, when the given accessory operates as the engine starter in a motor mode, it increases the degree of tension of the endless transmitting member between the driving pulley and the pulley of the given accessory, thereby moving the pulley of the first auto-tensioner to a limit of a relative movable range thereof. When the pulley of the first auto-tensioner reaches the limit of the relative movable range, the endless transmitting member rotates the driving pulley through its driving shaft to crank the internal combustion engine.
The power transmission system of the above publication is engineered to start operating the given accessory in the motor mode after it is required to start the internal combustion engine, thus taking time for the pulley of the first auto-tensioner to reach the limit of the relative movable range, thus resulting in a time lag in cranking the internal combustion engine.
When the internal combustion engine is being cranked, a difference in circumferential speed among the pulley of the given accessory, the driving pulley, and the first auto-tensioner will be great. Therefore, when the driving pulley and the pulley of the first auto-tensioner are started to be rotated suddenly by the pulley of the given accessory after they are stopped or when running at low speeds, the inertia thereof may result in a great increase in tension of the endless transmitting member. This requires the need for making the endless transmitting member of material resistant to such a degree of tension, which will lead to an increase in production cost of the power transmission system.
The power transmission system also faces the drawback in that when it is instructed to operate the given accessory in the motor mode after issuing of a request to start the internal combustion engine, it will result in a lag in producing a field current in the given accessory, thus leading to a delay in starting the given accessory in the motor mode. This also results in an increased lag in starting the internal combustion engine.